This invention relates to inkjet printing, and more particularly to ink containment and delivery systems.
Inkjet printing systems frequently make use of an inkjet printhead mounted to a carriage which is moved back and forth across a print media, such as paper. As the printhead is moved across the print media, control electronics activate an ejector portion of the printhead to eject, or jet, ink droplets from ejector nozzles and onto the print media to form images and characters. An ink supply provides ink replenishment for the printhead ejector portion.
Some printing systems make use of an ink supply that is replaceable separately from the printhead. When the ink supply is depleted, the ink supply is removed and replaced with a new ink supply. The printhead is then replaced at or near the end of printhead life and not when the ink supply is depleted. When a replaceable printhead is capable of utilizing a plurality of ink supplies, this will be referred to as a xe2x80x9csemipermanent xe2x80x9d printhead. This is in contrast to a disposable printhead, that is replaced with each container of ink.
To operate properly, many printheads must be maintained within a narrow range of slightly negative gauge pressure, typically between xe2x88x923 and xe2x88x9212 inches of water. Gauge pressure refers to a measured pressure relative to atmospheric pressure. Pressures referred to herein will all be gauge pressures. If the pressure becomes positive, printing and ink containment within the printhead will be adversely affected. During a printing operation, positive pressure can cause drooling and halt ejection of droplets. During storage, positive pressure can cause the printhead to drool. Ink that drools during storage can accumulate and coagulate on printheads and printer parts. This coagulated ink can permanently impair droplet ejection of the printhead and result in a need for costly printer repair. To avoid positive pressure, the printhead makes use of an internal mechanism to maintain negative pressure.
Air present in a printhead can interfere with the maintenance of negative pressure. When a printhead is initially filled with ink, air bubbles are often present. In addition, air accumulates during printhead life from a number of sources, including diffusion from outside atmosphere into the printhead and dissolved air coming out of the ink referred to as outgassing. During environmental changes, such as temperature increases or pressure drops, the air inside the printhead will expand in proportion to the total amount of air contained. This expansion is in opposition to the internal mechanism that maintains negative pressure. The internal mechanism within the printhead can compensate for these environmental changes over a limited range of environmental excursions. Outside of this range, the pressure in the printhead will become positive.
Moreover, if excessive air enters the printhead, this air can block air flow to the nozzles, interfering with drop ejection, and so degrading image quality.
An ink containment and delivery system in accordance with aspects of the invention provides high sustained flow rates, allows higher xe2x80x9cburstxe2x80x9d (short time interval) flow rates, and allows bubble movement through the system conduits to the printhead, all while holding the printhead ink pressure in a range required for optimum printhead operation. The ink containment and delivery system allows drool-free separability of the ink supply and the printhead.